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High performance metal-supported solid oxide fuel cells with Gd-doped ceria barrier layers
Technical University of Denmark.
Technical University of Denmark.
Y`Technical University of Denmark.
Technical University of Denmark.
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2011 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 196, no 22, 9459-9466 p.Article in journal (Refereed) Published
Abstract [en]

Metal-supported solid oxide fuel cells are believed to have commercial advantages compared to conventional anode (Ni-YSZ) supported cells, with the metal-supported cells having lower material costs, increased tolerance to mechanical and thermal stresses, and lower operational temperatures. The implementation of a metallic support has been challenged by the need to revise the cell fabrication route, as well as electrode microstructures and material choices, to compete with the energy output and stability of full ceramic cells. less thanbrgreater than less thanbrgreater thanThe metal-supported SOFC design developed at Riso DTU has been improved, and an electrochemical performance beyond the state-of-the-art anode-supported SOFC is demonstrated possible, by introducing a CGO barrier layer in combination with Sr-doped lanthanum cobalt oxide (LSC) cathode. Area specific resistances (ASR) down to 0.27 Omega cm(2), corresponding to a maximum power density of 1.14 W cm(-2) at 650 degrees C and 0.6 V. were obtained on cells with barrier layers fabricated by magnetron sputtering. The performance is dependent on the density of the barrier layer, indicating Sr(2+) diffusion is occurring at the intermediate SOFC temperatures. The optimized design further demonstrate improved durability with steady degradation rates of 0.9% kh(-1) in cell voltage for up to 3000 h galvanostatic testing at 650 degrees C and 0.25 A cm(-2).

Place, publisher, year, edition, pages
Elsevier , 2011. Vol. 196, no 22, 9459-9466 p.
Keyword [en]
SOFC, Metal-supported, Barrier layer, Magnetron sputtering, Durability
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-71631DOI: 10.1016/j.jpowsour.2011.07.014ISI: 000295602400048OAI: oai:DiVA.org:liu-71631DiVA: diva2:451839
Note

Funding Agencies|Topsoe Fuel Cell A/S||Danish National Advanced Technology Foundation||EU|FP7-211940 (METSOFC)|NordForsk|9346|

Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2017-12-08
In thesis
1. Physical Vapor Deposition of Yttria-Stabilized Zirconia and Gadolinia-Doped Ceria Thin Films for Fuel Cell Applications
Open this publication in new window or tab >>Physical Vapor Deposition of Yttria-Stabilized Zirconia and Gadolinia-Doped Ceria Thin Films for Fuel Cell Applications
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, reactive sputter deposition of yttria-stabilized zirconia (YSZ) and cerium gadolinium oxide (CGO) thin films for solid oxide fuel cell (SOFC) applications have been studied. All films have been deposited under industrial conditions.

YSZ films were deposited on silicon wafers as well as commercial NiO-YSZ fuel cell anodes. The texture, morphology, and composition of the deposited films were investigated with respect to deposition parameters such as bias voltage which was identified as a key parameter to tailor the texture of the film and promote less columnar coatings when depositing on Si. In contrast, films grown on NiO-YSZ fuel cell anodes were seen to be randomly orientated when deposited at low substrate bias voltages. When the bias voltage was increased the film took over the orientation of underlying substrate due to substrate template effects. The deposited coatings were found to be homogeneous large areas within the coating zone, which is highly important for industrial applications.

The performance of sputtered CGO thin films as diffusion barriers for stopping Sr diffusion between SOFC cathodes and electrolytes was also studied. This was done by introducing the sputtered CGO films in a metal-based SOFC setup. The performance depended on the density of the barrier layer, signifying that Sr diffusion and SrZrO3 formation is an issue. Area specific resistances down to 0.27 Ωcm2, corresponding to a maximum power density up to 1.14 W cm−2 at 650 °C could be obtained with sputtered CGO barrier layers in combination with Sr-doped lanthanum cobalt oxide cathodes which is a significant improvement compared conventional ceramic SOFCs.

The diffusion mechanism of Sr through sputtered CGO films was investigated. For this purpose, a model system simulating a SOFC was prepared by depositing CGO and YSZ on cathode material. This setup allowed observation of Sr diffusion by observing SrZrO3 formation using X-ray diffraction while annealing. Electron microscopy was subsequently performed to confirm the results. It was found that Sr diffused along column/grain boundaries in the CGO films but by modifying the film thickness and microstructure the breaking temperature of the barrier could be increased.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 40 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1552
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-84611 (URN)LIU-TEK-LIC-2012:37 (Local ID)978-91-7519-767-8 (ISBN)LIU-TEK-LIC-2012:37 (Archive number)LIU-TEK-LIC-2012:37 (OAI)
Presentation
2012-11-12, Planck, Fysikhusete, Campus Valla, Linköpings universitet, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2012-10-15 Created: 2012-10-15 Last updated: 2015-01-13Bibliographically approved
2. Yttria-Stabilized Zirconia and Gadolinia-Doped Ceria Thin Films for Fuel Cell Applications
Open this publication in new window or tab >>Yttria-Stabilized Zirconia and Gadolinia-Doped Ceria Thin Films for Fuel Cell Applications
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Solid oxide fuel cells convert chemical energy directly into electrical energy with high efficiency and low emission of pollutants. However, before fuel cell technology can gain a significant share of the electrical power market, the operation temperature needs to be reduced in order to decrease costs and improve the durability of the cells. Application of thin film electrolytes and barrier coatings is a way of achieving this goal.

In this thesis, I have investigated film growth and microstructure of yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (CGO) thin films deposited by physical vapor deposition. The aim is to make industrially applicable coatings suitable for application in solid oxide fuel cells (SOFCs). For this purpose, the coatings need to be thin and dense. YSZ coatings were prepared by pulsed direct current (DC) magnetron sputtering and high power impulse magnetron sputtering (HiPIMS) in both laboratory- and industrial-scale setups.

Industrial-scale pulsed DC magnetron sputtering of YSZ showed that homogenous coating over large areas was possible. In order to increase film density of the YSZ, HiPIMS was used. By tuning deposition pressure, peak power density and substrate bias voltage it was possible to deposit noncolumnar thin films without voids and cracks as desired for SOFC applications.

CGO coatings were deposited by pulsed DC magnetron sputtering with the purpose of implementing diffusion barriers to prevent reactions between Sr from the SOFC cathode and the electrolyte. A model system simulating a SOFC was prepared by depositing thin CGO and YSZ layers on cathode material. This setup allowed the study of Sr diffusion by observing SrZrO3 formation using X-ray diffraction while annealing. Electron microscopy was subsequently performed to confirm the results. The study revealed Sr to diffuse along column/grain boundaries in the CGO films but by modifying the film thickness and microstructure the breaking temperature of the barrier could be increased.

CGO thin films were implemented in metal-based SOFC and the influence of film microstructure and thickness on the electrochemical performance of the cell was studied. Cell tests showed that an area specific resistance (ASR) down to 0.27 Ωcm2 could be obtained 650 °C with sputtered CGO barrier layers in combination with a lanthanum strontium cobaltite cathode. In comparison a spin-coated CGO barrier resulted in an ASR value of 0.50 Ωcm2. This shows the high effectiveness of the sputtered barrier in obtaining state-of-the-art performance.

In summary, this work provides fundamental understanding of the deposition and growth of YSZ and CGO thins films and proves the prospective of employing thin film barrier coating in order to obtain high-performing SOFCs.  

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 63 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1564
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-102513 (URN)10.3384/diss.diva-102513 (DOI)978-91-7519-441-7 (ISBN)
Public defence
2014-02-25, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-12-12 Created: 2013-12-12 Last updated: 2015-01-13Bibliographically approved

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